Hi Tony and welcome, I have built a standup bass but I could not dig up [pun intended] a cigar box big enough. Serious though I have seen them on here. If I was doing one I would just put the box where the shovel is on the one pictured. How big and strong the box needs to be would depend on the design, number of strings bridge Hight and scale length and so on.
Wow that shovel one is impressively cool. Is that your design? Do you also sell these?
Additionally, I’ve seen uprights using a wine crate instead? Is this structurally similar?
I haven't built one myself but I have seen a few tea chest basses here in Australia and I think the yank equivalent is the washtub bass. I have read of suitcase upright basses.
I did one as a semi-normal cbg and ran the stick to the floor. It is a 2 string fretless. The stick for the lower half was a piece of hickory that was originally intended for a bow. The upper half is a 1x2 neck turned sideways. Tuned EA. Sounds like a bass but quieter as would be expected from a single box. It has a piezo if more sound is needed.
I made a 2 String tub bass with a 1"x 4"x 4' oak slab.I when with tub bottom and the back open tho I may close it and put sound holes no the front.I'v never play a upright so I when with a 30" scale from my bass
I'm building one from a wheelbarrow. My progress is here: https://cigarboxnation.com/photo/albums/cigarbox-style-wheelbarrow-...